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Element Z=117 Confirmed

Nuclear physicists have invested huge effort in creating superheavy elements, which consist of enough neutrons to provide enhanced stability from nuclear decay. For the past 30 years, experiments have been marching towards this “island of stability” with a new elemental discovery every 2 to 3 years. Part of the discovery process includes the confirmation by an independent experimental collaboration—it is only at this point that an element obtains its official status.

An international team using an intense 48Ca beam provided by GSI research facility in Darmstadt, Germany, and a target material of radioactive 249Bk supplied by Oak Ridge National Lab in Tennessee has produced two atoms of the superheavy element with atomic number Z=117, confirming the initial observation published in 2010 (see 9 April 2010 Viewpoint). In the process, a new isotope 266Lr was discovered from the previously unknown alpha-decay branch of 270Db. With a half-life of 1hour, 270Db is the longest-lived alpha emitter having an atomic number, Z, greater than 102.

The experiment is a tour de force in superheavy element research and required a detailed reconstruction of a seven-step alpha-decay chain followed by the spontaneous fission of the newly discovered 266Lr. The difficulty stems from the large variation in decay lifetimes along the alpha chain. The discovery was made feasible by the use of TASCA, a gas-filled recoil separator specifically designed for a high selectivity of superheavy or transactinide elements.